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ELECTRICITY

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					ELECTRICITY
                   Electricity

The Greeks discovered
 certain objects such as
 rods of amber could be
 rubbed with cat's fur
 and attract light objects
 like feathers.
                        Electricity Fundamentals
Atoms are neutrally charged
The nucleus is composed of protons and
    neutrons.
Neutrons have no charge
Protons are positively charged
Electrons in the orbitals are negatively
    charged
                               Electricity
Some electrons, particularly in metals are loosely bound and can detach
  and become “free electrons”

Free electrons as the name implies can move freely from atom to atom

When a force or pressure is applied free electrons begin to move
                              Electricity
   The materials that allow the free movement of electrons are called
    CONDUCTORS
   The following metals are considered as the best conductors:
     Gold
     Silver

     Copper

     Aluminum
                              Electricity
   Non Conductors or Insulators:
        Dry Wood
        Glass
        Rubber
        Mica
        Asbestos


   Semi-Conductors:
        Silicon
                         Electricity
For Charged Bodies

      +              +                 -      +


  Like charges repel             Unlike charges attract
                            Electricity
   Electrical energy is transferred through conductors by means of
    movement of free electrons
   A material’s ability to conduct current flow determines whether it
    is a good or bad conductor
                           Electricity
The force that moves electrons in a conductor can be called
Voltage

Electromotive Force

Potential Difference
                          Static Electricity
When an atom loses or gains electrons, it becomes positively or negatively
  charged, respectively.
When a material becomes charged it will keep its positive or negative
  charge as long as it stays isolated from other materials (Static Charge)
Once it comes in contact with another material the negative charge will
  flow to the positive.
                              CIRCUITS
In any electric circuit where electrons move around, three things are present:
     Voltage

     Current

     Resistance
                  VOLTAGE ( V or E)
Six Methods of Producing Voltage
Friction – Static electricity
Pressure – Compression of crystals
Heating – In copper electrons move away
   from the heat. In iron they move to the heat.
Light – Photoelectric cells
Chemical Action - Batteries
Magnetism
                 CURRENT (I)
Charges are measured in terms of Coulombs
  (C)
One electron has a charge of 1.602 x 10 -19 C
1 Coulomb = 6.28 x 1018 electrons
6,280,000,000,000,000,000 electrons

Ampere = 1 coulomb of charge flowing per
 second
       = basic unit of current
       =A
                RESISTANCE (R)

-   Measure of the opposition of the material to
    the flow of electrons.
-   Insulators have high resistance; conductors
    have low resistance.
-   Measured in terms of ohms (Ώ)
                                 OHM’S LAW
Ohms Law – The current in a circuit is
     directly proportional to the applied
     voltage and indirectly proportional to
     the circuits resistance.
                                                 E
                                              I
I = current measured in amperes (amps)
E = Voltage
R = Resistance in Ohms
                                                 R
                  OHM’S LAW APPLICATION


                              +
                    battery
                              -



Battery = 3 volts
Resistance = 1.5 ohms                E        3
                                  I      I
Amperes = ?                          R       1 .5
Amperes = 2
              OHM’S LAW TRIANGLE
Another way of writing ohms law:



                            E

                        I       R
               ELECTRIC POWER - WATTS
Watts is the name given to electrical flow – but what flows?
Energy
Energy is measures in joules

A joule of electrical energy can move from place to place along the
    wires.

The amount of energy that flows in one second is one watt.
        ELECTRIC POWER - WATTS

Power pertains to the rate at which work is
 being done.
Work is done whenever a force causes motion
  i.e. when voltage causes electrons to move
    in a circuit work is done
The rate at which this work is done is called
 the electric power rate and is measured in
 WATTS
            ELECTRIC POWER - WATTS
Watts = the amount of voltage across a circuit x the current
  through the circuit
                       or
                Watts = Amperes x Volts
                      or
                      P= I E
     ELECTRIC POWER - WATTS



      PI R              2

P = Power in watts
I = current in Amperes
R = resistance in ohms

				
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posted:1/15/2013
language:English
pages:21